The present invention relates to a diaphragm for electrolysis which has a base of fluorinated resins and is of a marked hydrophilic character, as well as the method of preparing this diaphragm.
For some years, the conventional asbestos diaphragms for electrolysis, deposited on the cathodes of cells intended, in particular, for obtaining chlorine and sodium hydroxide, have been progressively replaced by diaphragms having a base of fluorinated resins optionally containing reinforcing fibers. Such diaphragms have numerous advantages due, in particular, to the chemical properties of the fluorinated resins, but they also have a substantial disadvantage, also inherent in these resins, of poor wettability. This defect is attenuated to some extent when fibers such as asbestos are incorporated in large proportions in the diaphragms, but the hazards associated with this material are well known.
Numerous solutions have been proposed to overcome this drawback. In addition to the use of special fillers such as oxides or hydroxides of titanium, zirconium, or aluminum or asbestos, introduction of groups containing sulfur, particularly sulfonic groups, either by treatment in situ of the resin used (described in U.S. Pat. No. 4,153,520) or by addition of previously sulfonated resin (described in French Pat. No. 2,152,988) has been suggested.